N=gets.to_i
W=gets.split.map(&:to_i)
S=W.sum

if S%2==1
    puts "impossible"
    exit
end

S/=2
DP=Array.new(N+1,Array.new(N*N+1,0))
DP[0][0]=1

for i in 1..N do
    for j in 0..N*N do
        DP[i][j+W[i-1]]=1 if j+W[i-1]<=N*N && DP[i-1][j]==1
    end
end

puts "possible" if DP[N][S]==1
puts "impossible" if DP[N][S]!=1